There has been used a triacetyl cellulose (TAC) film having an in-plane retardation value of substantially zero, in order to protect a polarizing element. A polarizing element is usually sandwiched between two TAC films to form a polarizing plate. In recent years, protective films for polarizing plates, represented by TAC films, have also been provided with a role of a retardation film and these protective films have become more and more functionalized. Accordingly, an environmentally resistant polarizing plate has been demanded.
A technique for preventing deterioration of these films is important to improve environmental resistance of polarizing plates. For example, a technique for preventing deterioration due to irradiation of UV rays has been disclosed in Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) Nos. 2000-193821 and 2001-272682 in which an ultraviolet absorber has been used to protect the polarizing element.
Improvement in durability of a polarizing plate may also be attained by adding stabilizers (for example, an antioxidant, peroxide scavenger, radical scavenger, metal deactivator, acid trapping agent and amine). Examples of stabilizers have been disclosed in JP-A Nos. 3-199201, 5-1907073, 5-194789, 5-271471 and 6-107854.
For flat panel displays, for example, liquid crystal displays, organic electroluminescent displays and PDPs, there have been the following problems, for example: (i) diversification of display size (enlargement or a mobile application); and (ii) requirements for display qualities (contrast, hue control in color displays, high resolution and wide viewing angle in liquid crystal displays), and more improvement in quality is required.
In recent years, the viewing angle property of a TFT-TN mode liquid crystal display has been greatly improved by providing two films containing a discotic liquid crystalline compound plates on both surfaces of a liquid crystal cell as has been disclosed in JP-A No. 7-191217.
The viewing angle property has also been improved by an improvement in the liquid crystal mode itself. For example, a liquid crystal display using a vertical alignment (VA) mode liquid crystal cell has been disclosed in JP-A No. 2-176625, in which liquid crystalline compounds are basically vertically oriented when a voltage is not applied to the cell. A VA mode liquid crystal display enables observation of the display within a wider angle and also enable a higher speed switching rate of images compared to displays of conventional liquid crystal modes, however, more improvements compared to CRTs, specifically, in oblique observation from angles of 45°, 135°, 225° and 315°, are still being demanded. Use of viewing angle compensation films is highly expected to improve the viewing angle.
On the other hand, when displaying a halftone of a black level and a white level, there are some liquid crystalline compounds orienting oblique to the substrate. Accordingly, brightness of the display may also differ depending on the viewing direction. In a color display, this difference may even result in a difference of perceived color.
To attain a wider viewing angle and higher contrast despite the above problems, proposed has been a multi-domain liquid crystal display, in which one picture element is divided into a plurality of domains, orientation of liquid crystalline compounds in each domain being changed by applying different electrical fields. Examples of a method to produce a multi-domain liquid crystal cell include: (i) a mask-rubbing method in which rubbing is carried out while a mask is moving (see, for example, Non-Patent Document 1); (ii) a method in which a plurality of orientation materials are used (see, for example, Non-Patent Document 2); and (iii) a method in which characteristics of an orientation film is changed by irradiation of UV rays (see Patent Document 1).
An optical compensation film has been used to widen the viewing angle of a liquid crystal display together with the multi-domain technology and, further, it has been tested for use in a VA mode liquid crystal cell. A simultaneous use of an A plate and a C plate has been proposed (see, for example, Non-Patent Document 3).
Recently, since the market of liquid crystal displays is increasing, specifically for TVs in which moving pictures are displayed and for mobile displays which tends to be largely affected by the environment, development of a largely improved polarizing plate exhibiting an improved image quality and sufficient durability, together with a display having a improved polarizing plate are strongly demanded.
(Patent Documents 1)                JP-A No. 5-210099        
(Non-Patent Document 1) K. Takatori et al., “A Complementary TN LCD with Wide-Viewing Angle Grayscale”, Japan Display '92, p 591
(Non-Patent Document 2) T. Kamada et al., “Wide Viewing Angle Full-Color TFT LCDs”, Japan Display '92, p 886
(Non-Patent Document 3) J. Chen et al., SID '98 Digest, p 315